Added option for configuration file

[mjavier2k]

• added option to use config.yaml
• updated README.md

[mjavier2k]

implements #25

[neufeldtech]

How do the settings from viper get bound to the config variables?

[mjavier2k]

When viper.ReadInConfig() is called, it reads the config file which has the same key as whats on https://github.com/mjavier2k/solidfire-exporter/blob/master/pkg/solidfire/types.go#L8-L14

that becomes the default values for those KV pair which can be override by either flags or env.

[neufeldtech]

What I meant is that we're not doing any 'reading' of the viper config anywhere after it exists, i.e. viper.Get("endpoint")
We also need to consider the order of operations in terms of if flags will override the config file, etc. Viper could provide some help with this if we adopt the viper-native approach. If we're making breaking changes to the configuration anyway (by removing the option of passing username/password on the CLI via a flag), then we might as well adopt the viper-native approach where it can automatically 'detect' environment variables based on our go variable names, and automatically handle config file and flag order of operations.

[neufeldtech]

My Bad - I forgot that we are already using viper, so your config file pattern just magically works

solidfire-exporter/pkg/solidfire/solidfire.go

Lines 34 to 36 in ca5e825

	Username: viper.GetString(UsernameFlag),
	Password: viper.GetString(PasswordFlag),
	RPCEndpoint: viper.GetString(EndpointFlag),

[neufeldtech]

Do we want to drop support for passing in username/password as flags?

[mjavier2k]

Yeah, lets drop that support. i'll remove the username/password option on the command line flag

[neufeldtech]

Is there a need for a config flag for the config file itself?
I.e.

-c "path to config.yaml file" (Default ./something.yaml)

[neufeldtech]

If we remove these here, can we still pass username/password through an environment variable?
As I recall, we want to support username and password via an Environment variable or config file, but want to drop support for having them as command-line flags.

[mjavier2k]

Yup. thats what we want here. going to update this.

[neufeldtech]

This is the flag name not the flag's default value.

You probably meant this to be as such:

Suggested change

	ConfigFileFlag = "config.yaml"
	ConfigFileFlag = "config"